Tomosynthesis is used to create a three-dimensional image volume of a person's body part, e.g. her breast, or an object, using X-rays. Currently, tomosynthesis breast imaging is available only for research purposes, but an increasing number of market analysts believe it will become more widely used than conventional two-dimensional mammography.
Tomosynthesis is essentially a limited form of Computed Tomography or CT. Normally, several projection images, e.g. 5 or 30, are acquired in a range of different angles, e.g. −10 to +10 degrees. Each projection image is essentially a conventional 2-dimensional digital X-ray image of the examined object. The projection images are then combined using special purpose software for producing a 3-dimensional image volume, which is a 3-dimensional array of voxels, wherein each voxel is essentially a value corresponding to the X-ray attenuation in one point of the real world. The image volume may also be regarded as a stack of layers or slices, wherein each layer or slice is a 2-dimensional image, which can be displayed as normal image. By definition, the layers are oriented essentially orthogonal to the x-ray beams, or in other words such that they are essentially parallel to the projection images. An un-trained viewer may feel that each layer looks like a projection image; despite it is essentially an extraction of structures at a certain depth in the breast. Typically, the thickness of each layer is about 1 to 2 mm, and the pixel size in each layer is 0.05 to 0.2 mm.
Biopsy is a method for extracting tissue from a breast. It is widely used to extract parts of suspected tumors, in particular micro-calcifications. Most commonly, biopsy is performed using stereo-tactic imaging, wherein two 2-dimensional images projection images are acquired from different angle. The operator selects the same target position (most often a microcalc) in both images and a computer determines the three-dimensional coordinates. In most cases, a needle is inserted through a hole in the compression paddle, whereby the breast deformation moves the micro-calcification close to the point of skin penetration. There are also cases where the needle is inserted from directions along the compression paddle, but that implies a longer distance for the needle to travel through the breast.
Speed is important, since biopsy is uncomfortable for the patient, who has her breast compressed and a needle inserted. Most clinics use the same x-ray apparatus for biopsy as for regular mammography examinations, which implies that the patient has to sit on a chair in an upright position during the examination. It happens that patients faint during examination.